Address 6 on the Ambika SPI bus?

I was browsing through the Ambika technical notes, and noticed this in the section about the SPI bus: “…an expansion port used for future peripherals/controllers (address 6)”.

Has any use been made of this spare address on the bus, or could some use be made of it? I know that there is almost no space left on the controller for additional code without omitting other features, and that SPI is only intended for local communications, so whatever was driven or read would need to be very close, and not sure how hard it would be to connect to the 4 SPI lines in the connection header. Just wondering.

there was some plans for a nunchuck controller interface at the time of the pioneer run. but i think it never got finished.
see here: